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*usr_29.txt*	For Vim version 8.2.  Last change: 2016 Feb 27

VIM USER MANUAL - by Bram Moolenaar

Moving through programs

The creator of Vim is a computer programmer.  It's no surprise that Vim
contains many features to aid in writing programs.  Jump around to find where
identifiers are defined and used.  Preview declarations in a separate window.
There is more in the next chapter.

|29.1|	Using tags
|29.2|	The preview window
|29.3|	Moving through a program
|29.4|	Finding global identifiers
|29.5|	Finding local identifiers

==============================================================================
*29.1*	Using tags

What is a tag?  It is a location where an identifier is defined.  An example
is a function definition in a C or C++ program.  A list of tags is kept in a
tags file.  This can be used by Vim to directly jump from any place to the
tag, the place where an identifier is defined.
   To generate the tags file for all C files in the current directory, use the
following command: >

ctags *.c

"ctags" is a separate program.  Most Unix systems already have it installed.
If you do not have it yet, you can find Exuberant ctags here:

http://ctags.sf.net ~

Now when you are in Vim and you want to go to a function definition, you can
jump to it by using the following command: >

:tag startlist

This command will find the function "startlist" even if it is in another file.
   The CTRL-] command jumps to the tag of the word that is under the cursor.
This makes it easy to explore a tangle of C code.  Suppose, for example, that
you are in the function "write_block".  You can see that it calls
"write_line".  But what does "write_line" do?  By placing the cursor on the
call to "write_line" and pressing CTRL-], you jump to the definition of this
function.
   The "write_line" function calls "write_char".  You need to figure out what
it does.  So you position the cursor over the call to "write_char" and press
CTRL-].  Now you are at the definition of "write_char".

+-------------------------------------+
	|void write_block(char **s; int cnt)  |
	|{				      |
	|   int i;			      |
	|   for (i = 0; i < cnt; ++i)	      |
	|      write_line(s[i]);	      |
	|}	    |			      |
	+-----------|-------------------------+
		    |
	     CTRL-] |
		    |	 +----------------------------+
		    +--> |void write_line(char *s)    |
			 |{			      |
			 |   while (*s != 0)	      |
			 |	write_char(*s++);     |
			 |}	  |		      |
			 +--------|-------------------+
				  |
			   CTRL-] |
				  |    +------------------------------------+
				  +--> |void write_char(char c)		    |
				       |{				    |
				       |    putchar((int)(unsigned char)c); |
				       |}				    |
				       +------------------------------------+

The ":tags" command shows the list of tags that you traversed through:

:tags
	  # TO tag	   FROM line  in file/text ~
	  1  1 write_line	   8  write_block.c ~
	  2  1 write_char	   7  write_line.c ~
	> ~
>
Now to go back.  The CTRL-T command goes to the preceding tag.  In the example
above you get back to the "write_line" function, in the call to "write_char".
   This command takes a count argument that indicates how many tags to jump
back.  You have gone forward, and now back.  Let's go forward again.  The
following command goes to the tag on top of the list: >

:tag

You can prefix it with a count and jump forward that many tags.  For example:
":3tag".  CTRL-T also can be preceded with a count.
   These commands thus allow you to go down a call tree with CTRL-] and back
up again with CTRL-T.  Use ":tags" to find out where you are.

SPLIT WINDOWS

The ":tag" command replaces the file in the current window with the one
containing the new function.  But suppose you want to see not only the old
function but also the new one?  You can split the window using the ":split"
command followed by the ":tag" command.  Vim has a shorthand command that does
both: >
	:stag tagname

To split the current window and jump to the tag under the cursor use this
command: >

CTRL-W ]

If a count is specified, the new window will be that many lines high.

MORE TAGS FILES

When you have files in many directories, you can create a tags file in each of
them.  Vim will then only be able to jump to tags within that directory.
   To find more tags files, set the 'tags' option to include all the relevant
tags files.  Example: >

:set tags=./tags,./../tags,./*/tags

This finds a tags file in the same directory as the current file, one
directory level higher and in all subdirectories.
   This is quite a number of tags files, but it may still not be enough.  For
example, when editing a file in "~/proj/src", you will not find the tags file
"~/proj/sub/tags".  For this situation Vim offers to search a whole directory
tree for tags files.  Example: >

:set tags=~/proj/**/tags

ONE TAGS FILE

When Vim has to search many places for tags files, you can hear the disk
rattling.  It may get a bit slow.  In that case it's better to spend this
time while generating one big tags file.  You might do this overnight.
   This requires the Exuberant ctags program, mentioned above.  It offers an
argument to search a whole directory tree: >

cd ~/proj
	ctags -R .

The nice thing about this is that Exuberant ctags recognizes various file
types.  Thus this doesn't work just for C and C++ programs, also for Eiffel
and even Vim scripts.  See the ctags documentation to tune this.
   Now you only need to tell Vim where your big tags file is: >

:set tags=~/proj/tags

MULTIPLE MATCHES

When a function is defined multiple times (or a method in several classes),
the ":tag" command will jump to the first one.  If there is a match in the
current file, that one is used first.
   You can now jump to other matches for the same tag with: >

:tnext

Repeat this to find further matches.  If there are many, you can select which
one to jump to: >

:tselect tagname

Vim will present you with a list of choices:

# pri kind tag	       file ~
	  1 F	f    mch_init	       os_amiga.c ~
		       mch_init() ~
	  2 F	f    mch_init	       os_mac.c ~
		       mch_init() ~
	  3 F	f    mch_init	       os_msdos.c ~
		       mch_init(void) ~
	  4 F	f    mch_init	       os_riscos.c ~
		       mch_init() ~
	Enter nr of choice (<CR> to abort):  ~

You can now enter the number (in the first column) of the match that you would
like to jump to.  The information in the other columns give you a good idea of
where the match is defined.

To move between the matching tags, these commands can be used:

:tfirst			go to first match
	:[count]tprevious	go to [count] previous match
	:[count]tnext		go to [count] next match
	:tlast			go to last match

If [count] is omitted then one is used.

GUESSING TAG NAMES

Command line completion is a good way to avoid typing a long tag name.  Just
type the first bit and press <Tab>: >

:tag write_<Tab>

You will get the first match.  If it's not the one you want, press <Tab> until
you find the right one.
   Sometimes you only know part of the name of a function.  Or you have many
tags that start with the same string, but end differently.  Then you can tell
Vim to use a pattern to find the tag.
   Suppose you want to jump to a tag that contains "block".  First type
this: >

:tag /block

Now use command line completion: press <Tab>.  Vim will find all tags that
contain "block" and use the first match.
   The "/" before a tag name tells Vim that what follows is not a literal tag
name, but a pattern.  You can use all the items for search patterns here.  For
example, suppose you want to select a tag that starts with "write_": >

:tselect /^write_

The "^" specifies that the tag starts with "write_".  Otherwise it would also
be found halfway a tag name.  Similarly "$" at the end makes sure the pattern
matches until the end of a tag.

A TAGS BROWSER

Since CTRL-] takes you to the definition of the identifier under the cursor,
you can use a list of identifier names as a table of contents.  Here is an
example.
   First create a list of identifiers (this requires Exuberant ctags): >

ctags --c-types=f -f functions *.c

Now start Vim without a file, and edit this file in Vim, in a vertically split
window: >

vim
	:vsplit functions

The window contains a list of all the functions.  There is some more stuff,
but you can ignore that.  Do ":setlocal ts=99" to clean it up a bit.
   In this window, define a mapping: >

:nnoremap <buffer> <CR> 0ye<C-W>w:tag <C-R>"<CR>

Move the cursor to the line that contains the function you want to go to.
Now press <Enter>.  Vim will go to the other window and jump to the selected
function.